Industrial waste water contains a wide variety of pollutants that must be removed prior to the discharge of the waste water into the environment. A particularly toxic component in industrial waste water is the transition metal mercury. By means of flue gas desulfurization plants which are common in modern power plants that burn fossil fuels, mercury is removed from the combustion exhaust gases and finds its way into the waste water discharged from a flue gas desulfurization plant.
Selenium is an essential trace element, but in higher concentrations is very toxic, which is why there is an effort to remove selenium from waste water of industrial plants.
For example, in Germany, the discharge limit of mercury in the waste water of flue gas desulfurization plants is explicitly laid out in Waste Water Regulation 47, “Scrubbing of Flue Gases from Combustion Plants.” In its current form, published on Jun. 14, 2004, the limit for mercury is pegged at 30 μg/L. Allowable discharge limits for selenium are not stipulated by the current aforementioned regulation.
In the United States efforts to curb the discharge limits of mercury and selenium in waste water from industrial facilities, particularly in conventional power plants, are already taking place. In many cases, these limits have been set at <12 ppt (ng/L) for mercury and <6 ppb (μg/L) for selenium.
It is therefore the objective of the present invention to provide the industry with a commercial economically feasible method for removing mercury and selenium from sulfate-containing waste water.